These days, imaging plates are used for recording x-ray images within the scope of x-ray technology, in particular dental x-ray technology. These imaging plates comprise a phosphor material which is embedded in a transparent matrix. As a result, so-called storage centers arise, which can be converted by incident x-rays into excited metastable states. If such an imaging plate is exposed within an x-ray installation, for example for recording a bitewing of a patient, the imaging plate obtains a latent x-ray image in the form of excited and non-excited storage centers.
For the purposes of reading the imaging plate, the latter is scanned point-by-point with readout light in a scanning apparatus, as a result of which the metastable states of the excited storage centers are brought into a state which quickly relaxes under the emission of fluorescence light. This fluorescence light can be captured with the aid of a detector unit such that the x-ray image can be made visible using appropriate evaluation electronics.
Conventional scanning apparatuses, such as e.g. a drum scanner, guide the imaging plate along a cylindrical area over a readout gap. In the interior of the cylinder area, a rotating mirror is provided as a deflection unit, said rotating mirror producing a circulating readout beam. This readout beam passes through the readout gap onto the imaging plate and reads the latter point-by-point. At the same time, the imaging plate is guided past the readout gap by way of a mechanical drive such that the entire area of the imaging plate is captured.
Usually, the imaging plate is read with preset or structurally predetermined fixed readout parameters. Readout parameters include, for example, the dimension of the readout spot, i.e., for example, the focal dimension, on the imaging plate, the laser intensity of the excitation laser, gain, sensitivity and characteristic of the image receiver, and the integration time per pixel. A consequence of this is that an ideal image quality cannot be obtained in the case of strongly changing recording conditions. By way of example, it is not possible to react to an overexposure or underexposure of an imaging plate or to a large dynamic range within the image situated on an imaging plate. One possible remedy lies in correcting the read image by way of subsequent image processing. However, this may lead to increased image noise or image artifacts under certain circumstances. Alternatively, the entire dynamic range of the system can be increased. However, this is often not realizable from an economical or technical point of view.